1. Field of the Invention
This invention relates to an information recording and reproducing system for a data storage apparatus and more particularly to a positioning system for track location of a transducer. Still more particularly, it relates to a system for detecting the displacement of a transducer from a guide path which the transducer is to follow, by processing a train of positioning signals induced in the transducer by sensing magnetic transitions formed on servo-tracks.
2. Description of the Prior Art
A rotatable storage device, such as a magnetic disc storage, comprises a storage medium having a number of data tracks thereon, a transducer movable by an actuator over the data tracks from one transducing position to another, and a servo-system for providing the actuator with positioning signals. Since the use of transitions (magnetic flux reversals) was adopted, the field of the positioning servo-system has been increasingly extended and more accurate positioning of the transducer over the data tracks is required as the recording density on the magnetic disc has increased.
In a rotatable storage apparatus, a transducer is positioned over a guide path such as a borderline between two adjacent servo tracks. Each servo track has a series of magnetized domains arranged in series in the longitudinal (running) direction and has a magnetic orientation alternately in one direction and the opposite direction, forming magnetic transitions between two adjacent domains. Accordingly, the transducer gap, positioned over a running servo track, experiences a magnetic reversal each time a transition passes beneath the transducer gap and a series of pulses forming a pulse train, is induced in the transducer. The polarity and magnitude of the pulses depends upon the flux reversal thus induced. It should be noted that there is a group of transitions S having the same orientation formed on all tracks and aligned on the same radial of the disc which forms a continuous transition line. Therefore, at this point, a synchronizing pulse signal S having a fixed magnitude is induced regardless of the displacement of the transducer off its guide path. The pulse induced by the transition S is utilized as a clock pulse for the system.
At the other transitions for each servo track, positioning signals are induced in the transducer. The pulse magnitude of each signal is proportional to the width of a portion of the transducer which passes across the transition. As a result, the magnitude of each signal varies in proportion to the displacement of the transducer with respect to the guide path. Accordingly, the difference in the magnitude of two pulses, induced from two servo tracks adjacent to the guide path, can be utilized as positioning error information.
Positioning signals in a positioning system which had been generated with analog processing in the prior art systems had an inherent problem in that a complicated and expensive digital to analog convertor was required. However, recently, digital devices, such as digital large scale integrated circuits (LSI), have made a great improvement in high speed operation and high density packaging, and the operation is significantly faster than the prior analog devices. The use of such digital devices is favorable for high speed processing and miniaturization of the apparatus. Particularly, a great amount of software is applicable to construction of a system for a storage apparatus. Recently, a system providing digital positioning signals in pulse form to a servo system has been proposed. Such an approach is disclosed, for instance, in U.S. Pat. No. 4,157,577 entitled "Rotatable Storage Apparatus with Digitally Responsive Circuitry for Track Selection" issued in June, 1979, to Townsend H. Porter, Jr., et al.
The apparatus of this patent has a pair of groups consisting of different digital bytes, which are arranged in a stepwise pattern radially (perpendicular to the guide path, inside and outside of a guide path) on a magnetic disc. Error signals are obtained by detecting the number of bytes passing beneath the transducer. The number varies in proportion to the displacement of the transducer from the guide path. Thus the positioning error signals are fed to a servo system in a digital form. However, the configuration of the digital bytes is complicated and the number of steps in the signal is limited because of the limited space on the magnetic disc and the fabricating accuracy of the pattern, resulting in insufficient accuracy and a high fabricating cost of the device.